A. Introduction: The importance of sleep to proper health has emerged in recent years. The range of sleep disorders in children is broad, although the relevance of sleep to normal development and chronic illness is not well understood. Recently, critical roles for sleep in learning, memory, neurogenesis, and neural plasticity have been described, underlying the importance of sleep to brain function and brain development1. Consistently, sleep disturbances (sleep apnea, insomnia, sleepwalking, night terrors, confusional arousals, periodic limb movements (PLMS), and bruxism) have significant adverse effects on the quality of life of children and their families. Individuals with neurological disease are at particular risk because sleep disruptions lead to exacerbation of daytime behaviors and result in poor cognitive performance2. It is important to understand the nature of sleep impairments in children with neurological disorders, since this may have important implications for the degree of impairment of quality of life and intellectual functioning. Any understanding between sleep problems and behavioral disturbances would aid such understanding. The prevalence of sleep problems in the normal population is estimated to be between 18-37% in different studies3'4. Questionnaire and interview based studies among mentally retarded subjects show that approximately 15-50% of adults and 30-67% of children have sleep problems5'6 There are very little data on sleep abnormalities in Angelman syndrome (AS), Rett syndrome (RTT), and Prader-Willi syndrome (PWS).